Dynamo-electric machine



Fig.1.

S. R. BERGMAN.

DYNAMO ELECTRIC MACHINE.

APPLICATION FILED JUNE 20, I919- Patented May 11, 1920.

2 SHEETS-SHEET 3- Fig.2.

Inventor:

Sven R. Bergman,

by h M His Attorn ey.

S. R. BERGMAN.

DYNAMO ELECTRIC MACHINE.

APPLICATION FILED JUNE 20. 1919.

1,340,004. I Patented May 11,1920.

2 SHEEIS-SHEET 2.

0 20 40 v0 80 I00 /20 /40 /I0 /J0 200 220 240 260 280 Inventor:

Sven R.Ber-gma-n, y flw/ M His Attovne y.

1407 0 eras UNITED STATES PATENT OFFICE.

SVEN R. BERG-MAN, OF NAHANT, MASSACHUSETTS, ASSIGNOR '10 GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

DYNAMO-ELECTRIC MACHINE.

Specification of Letters Patent.

Patented May 11, 1920.

Application filed June 20,1919. Serial No. 305.554.

To all whom it may concern:

Be it known that I, SvEN R. BERGMAN, a

subject of the King of Sweden, residing at Nahant,-'in the county ofEssex, State of Massachusetts, have invented certain new and usefulImprovements in Dynamo-Electric Machines, of which the following is aspecification. My invention relates to dynamo-electric machinesandparticularly to dynamo-electric machines which supply electricalenergy at different potentials, depending upon the load.

My invention is especially applicable to dynamo-electric machines whichsupply electrical energy for arc welding. In order to obtain the bestresults in arc welding a peculiar voltage-current characteristic of thesource supplying electrical energy to the arc is required. If anelectric arcis fed from a constant potential source, the action of thearc is very erratic, because the resistance of an arc decreases with anincrease in current which results in a tendency for the current tobecome infinite if the potential across the terminals of the arc ismaintained constant. Similarly if the current in the arc begins todecrease'the resistance thereof increases and if a constant potential ismaintained across the terminals of the arc, a further decrease in thecurrent results until the arc goes out.

It is, therefore, desirable'to have an arrangement which will cause thevoltage across the terminals of the arc to decrease as the current inthe arc increases so as to overcome thetendency of the current toapproach an infinite value, and which will cause the voltage across theart to increase as the current in the arc decreases, in other words, anarrangement for automatically keeping the energy at the aresubstantially constant within limits.

It is also necessary to limit the maximum current on short-circuit so asto prevent 'excessive heating and the maximum voltage v on open circuitso. as to protect the welder from injury and .prevent the drawing of toolong an arc.

The object of my lnvention 1s to provide ing in a field. structurecomprising '2 n mechanical poles, arranged in two sets with an equalnumber of poles in each set, with adjacent poles in the separate setsarranged to be of like polarity. At least three brushes are arranged tobear upon the commutator, thisbeing the smallest number possible with atwo pole armature. I am thus enabled to derive from the armature threeelectromotive forces, one of which is the resultant of the other two.Two of the brushes are spaced substantially 180 electrical degrees apartand arranged with respect to said poles so that the voltage between saidbrushes is dependent on the flux in both sets of poles. One set of polesis arranged to produce a voltage between the third brush and one 180degree brush and the other set is arranged to produce a voltage betweenthe third brush and the other of the 180 degree brushes. By constructinga machine in this way, and properly controlling the flux in each set ofpoles the machine may be designed with any desired operatingcharacteristic. This type of dynamo electric machine is disclosed andclaimed broadly in my application Serial No. 112,940, filed August 3,1916. The voltage between the 180 degree brushes, for example, is equalto the algeb aic sum of the voltages induced in the arma e by therespective sets of poles and by arranging the sets of poles to producevoltages varying at difi'e'rent rates with variations in the output ofthe machine I am enabled by the inherent action of the machine to supplya load circuit connected to these brushes with a voltage which variesinversely with the current while at the same time the open circuitvoltage and the short circuit current are limited to any desired values.In the preferred embodiment of my invention, I arrange one set of polesto be substantially saturated so that means (not shown) such forexample, as an.

the flux therein is substantially unaffected by armature reaction, andthe voltage induced by this set of poles substantially constant at anygiven speed. I operate the other set of poles unsaturated and arrangethem so that the flux therein is varied in amount and direction by thearmature reaction due to load current, the arrangement being such thatthe voltage between the load brushes decreases when the load currentincreases.

Other features of novelty which characterize my invention are pointedout with particularity in the claims annexed to and forming a part ofthis specification. For a better understanding of my invention referencemay be had to the following descrip-' tion taken in connection with theaccompanying drawing in which Figures 1 to 5 inclusive showdiagrammatically several embodiments of m an ex lanatory 'a-gram.

Re erring to Fig. 1 of the drawing, 1 is the armature of adynamo-electric machine having a commutator 2 on which bear the loadbrushes or sets of brushes 3 and 13 which are placed 180 electricaldegrees apart, and an auxiliary brush or set of brushes 4 locatedbetween the load brushes. The armature 1 is preferably rotated atsubstantially constant speed by any well known induction motor,synchronous motor, D. C. shunt or compound motor, or other drivingmeans.

' A field magnet str cture having two sets of field poles 6 and Tsurround the armature. The field poles 6 are arranged to produce avoltage between the auxiliary brush 4 and the load brush 3, and thefield poles 7 are arranged to produce a voltage between the auxiliarybrush 4 and the load brush 13. Preferably the voltagebetween brushes- 4and 3 remains substantially constant, and the voltage between brushes 4and 13 varies with the load current. The voltage between the loadbrushes 3 and 13 isequal to the algebraic sum of the voltages betweenbrushes 4 and 3 and brushes 4 and 13. In order that the voltage producedin that part of the armature connected between brushes 4 add 3 by thepoles 6 shall remain substantially constant, the poles 6 arearinvention, and Fig. 6 is Arrows indicate the direction of the fluxproduced by the various windings on the drawings. The armature ispreferably series wound and has one-half as many poles as the fieldstructure, that is, the number of poles in the armature corresponds tothe number of poles in each set of the field poles. The arc weldingequipment indicated at 16 is connected across the mains which areconnected to the load brushes 3 and 13.

The operation of the dynamo-electric machine of F ig: 1 is as follows:Since the field magnetic circuit comprising the poles 6 is saturated,the voltage generated in the armature due to the flux in these poles,that is, that portion ofthe armature connected between auxiliary brush 4and load brush 3 is substantially constant, and since the windings 8 areconnected between these brushes the exciting current also remainsconstant.

Since the load current is taken from the main brushes 3 and 13 thereexists an arma; ture reaction AR which is substantially in line withthese brushes. This armature reaction AR may be resolved into twocomponents AD and AE. Since the magnetic circuit comprising poles 6 issaturatedthe component AD will not set up any additional flux therein. IThe component AE however will set up a flux through the field poles 7 insuch a direction that the voltage generated between brushes-4 and 13 isof opposite polarity to the voltage generated between brushes 4 and 3.Since the voltage between the load brushes 3 and 13 is equal to thealgebraic sum of the voltages between brushes 4 and 3 and brushes 4 and13 the line voltage is equal to the voltage between brushes 4 and 3minus the voltage between brushes 4 and 13, the machine can be sodesigned that the no-load voltage can Since the armature Y shown in Fig.2; These series windings are wound so as to aid the component AE of thearmature reaction.- It will be apparent that by changing the number ofturns of the series windings 10 any desired rate of change in thevoltage between brushes 4 and 13 can be obtained. It is preferabletherefore to provide the series winding 10 with a number of taps so thatthe rate can be readily changed.

Fig. 3 shows a modification of the machine shown in Fig. 1. In thisfigure the field poles 7 are provided with shunt windings 9 connected inseries with the shunt windings 8 on the field poles 6. Since the set upby them is in opposition to the com- )onent AE of the armature reaction.herefore, at no-load, the voltage between the load brushes 3 and 13 isequal to the voltage between brushes 3 and 4 plus the voltage 4- and 13.When, however, current is being supplied to the arc welding equipment 16the component AE diminishes the flux through the magnetic circuitcomprising the field poles 7 which results in a drop in the voltagebetween brushes 4 and 13 causing a corresponding drop in the voltagebetween brushes 3 and 13.

Since the armature reaction is usually not strong enough to obtain thedesired regulation it is preferableto place the series windings 10 onthe field poles 7, these series windings being wound in the same manneras in Fig. 2' so that the flux set up thereby ,is in such a direction asto aid the component AE of the armature reaction. Fig. 4 shows a machinewoundin this manner. It will be noticed that the poles 7 carry acompound excitation, the shunt windings 9 and the series windings 10acting diiferentially. These windin s are so wound that at a cerainvalue of oad current, preferably about half load, the resultant flux inthe poles 7 is zero. Then the voltage between the load brushes 3 and 13is equal to the voltage between brushes 3 and 4 because the voltagebetween brushes 4 and 13 is zero at this time. When the line currentincreases above this value the resultant flux in the poles 7 builds upin the opposite direction so that the voltage between brushes 4 and 13increases but with the, opposite polarity to that between brushes 3 and4. Therefore the voltage between brushes 3 and 13, instead of beingequal to the voltage between brushes 3 and 4 plus the voltage betweenbrushes 4 and 13, is equal to the voltage be-- tween brushes 3 and 4minus the voltage between brushes 4 and 13. My machine is so designedthat when the load circuit is shortcircuited, the voltage betweenbrushes 3 and 4 is substantially equal to the voltage bev6 tained inthis way.

tween brushes 4 and 13.

In order to obtain perfect commutation,

' commutating poles 14 provided with windings 15 connected in serieswith the armature may be added as shown in Fig. 5. The

commutating poles do not interfere with the regulation and are merelyadded in order to eliminate sparking. It has been found in practice thatperfect commutation can be ob- In order that a large number of weldingcurrents can be obtained from a single machine, it is, preferable toprovide the series windings 10 with a number of taps, as

shown in Figs. 2, 4 and 5. It will be evident that if only a smallnumber of turns of the series winding are used a'much larger currentwill have to flow to produce the necessary flux in poles 7 to give thedesired regulation than in the case where a large number of turns of theseries winding are used. By selecting the proper taps, any desiredweldin obtained. 'Flg. 6 shows the voltage-current characteristics of amachine when a different number of series turns are used. Curve A- isthe voltage-current curve'of the ma chine when no .series turns areused, curve B is the voltage-current curve when a few seriesturns areused. Curve C, D, E and F are similar curves where a larger number 1. Ina dynamo electric machine, an armature provided with a commutator, loadbrushes'and an auxiliary brush bearing on said commutator, a fieldmagnet structure having two sets of field poles, one of said sets ofpoles being saturated so that the flux in said set is unaffected byarmature reaction and produces a constant voltage between said auxiliarybrush and one of said load brushes, and the other of said sets of polesbeing unsaturated so that the flux therein is varied by the armaturereaction so that the voltage produced between the load brushes decreaseswhen the load current increases-the voltages between the load brushesbeing equal to the algebraic sumof the voltages between said auxiliarybrush and each of said load brushes and an exciting winding for saidsaturated poles connected between said auxiliary brush and one 1 between---said auxiliary brush and one of said load brushes, the otherof saidsets of poles being unsaturated so that the flux therein is varied bythe armature reaction so that the voltage produced between thecurrentwithin limits can be.

by Letters Patent of the UnitedStates, is

load brushes decreases when the load current increases, the voltagesbetween the load brushes being equal to the algebraic sum of thevoltages between said auxlhary brush and each of said load brushes, anexciting winding for said saturated poles connected between saidauxiliary brush and one of said load brushes, and field windings on saidunsaturated field poles wound so as to set up flux therein in the properdirection to aid the flux produced by the armature reaction.

3. In a dynamo electric machine, an armature provided with a commutator,load brushes and an auxiliary brush bearing on said commutator, a fieldmagnet structure having two sets of field poles, one of said sets ofpoles bein saturated so that the flux in said set is una ected byarmature reaction and produces a constant voltage between said auxiliarybrush and one of said load brushes, the other of said sets of polesbeing unsaturated so that the flux therein is varied by the armaturereaction so that the voltage produced between the load brushes decreaseswhen the load current increases, the voltages between said load brushesbeing equal to the algebraic sumof the voltages between said auxiliarybrush and each of said load brushes, and field windings on saidunsaturated field poles connected betwen said auxiliary brush andoneof-said load brushes and arranged to set up a constant fiux in saidpoles in an opposite direction to the flux produced in said poles byarmature reaction.

4. In a dynamo electric machine, an armature provided with a commutator,load brushes and an auxiliary brush bearing on said commutator, a fieldmagnet structure havin two sets of field poles, one of said sets 0 polesbein saturated so that the flux in said set is una ected by armaturereaction and produces a constant voltage between said auxiliary brushand one of said load brushes, the other of said sets of poles beingunsaturated so that the flux therein is varied by the armature reactionso that the voltage produced between the load brushes decreases when theload current increases, the

' voltage between said load brushes being unsaturated field polesconnected in series with the armature and wound differentially withrespect to the first mentioned field windings.

I 5. In a dynamo electric machine, an

armature provided with a commutator, load brushes and an auxiliary,brush bearing on said commutator, a field magnet structure having twosets of field poles, one of said and each of said load brushes, fieldwindings for all of said poles connected between said auxiliary brushand one of said load brushes, the field windings on said unsaturatedpoles being arranged to set up a flux in an opposite direction to theflux produced in said poles by armature reaction.

6. In a dynamo electric machine, an armature provided with a commutator,load brushes and an auxiliary brush bearing on said commutator, a fieldmagnet structure having two sets of field poles, one of said sets ofpoles being saturated so that the flux in said set is unaffected byarmature reaction and produces a constant voltage between said auxiliarybrush and one of said load brushes, the other of said sets of polesbeing unsaturated so that the flux therein is varied by the armaturereaction so that the voltage produced between the load brushes decreaseswhen the load current increases, the voltages between the load brushesbeing equal to the algebraic sum of the voltages between said auxiliarybrush and each of said, load brushes, field windings for all of saidpoles connected between said auxiliary brush and one of said loadbrushes, the field windings on said unsaturated poles being arranged toset up a flux in an opposite direction to the flux produced in saidpoles by armature reaction, and other field windings on said unsaturatedpoles connected in series with the armature and wound difierentiallywith respect to first mentioned field windings.

7. In a dynamo electric machine, an armature provided with a commutator,load brushes and an auxiliary brush bearing on said commutator, a fieldmagnet structure having two sets of field poles, one of said sets ofpoles beingsaturated so that the flux in said set is unaffected byarmature reaction and produces a constant voltage between said auxiliarybrush and one of said load brushes, the other .of said sets of polesbeing unsaturated so that the flux therein is varied by the armaturereaction so that the voltage produced between the load brushes decreaseswhen the load current increases, the voltages between the load brushesbeing equal to the algebraic sum of the voltages between said auxiliarybrush and each of said load brushes, and field reaper windings. for allof said poles connected between said auxiliary brush and one of saidload brushes and across that portion of the armature which has a voltageinduced therein by the saturated poles, the field windings on saidunsaturated poles being arranged to set up a flux in an oppositedirection to the fiux produced in said poles by armature reaction.

8. In a dynamo electric machine, an armature provided with a commutator,load brushes and an auxiliary brush bearing on said commutator, a fieldmagnet structure having two sets of field poles, one of said sets ofpoles being saturated so that the flux in said set is unafiected byarmature reaction and produces a constant voltage between said auxiliarybrush and one of said load brushes and the other of said sets of polesbeing unsaturated so that the flux therein is varied by the armaturereaction so that the voltage produced between the load brushes decreaseswhen the load current increases, the voltages between the load brushesbeing equal to the algebraic sum of the voltages between said auxiliarybrush and each of said load brushes, field windings for all of saidpoles connected between i said auxiliary brush and one of said loadbrushes and across that portion of the armature which has a voltageinduced therein by the saturated poles, the fieldwindings on saidunsaturated poles being arranged to set up a flux in an oppositedirection to the flux produced in said poles by armature reaction, andother'field windings on said unsaturated poles connected in series withthe armature and wound differentially with respect to first mentionedfield windings.

9. In a constant speed dynamo-electric machine, an armature providedwith a commutator, load brushes and an auxiliary brush bearing on saidcommutator, a fieldmagnet structure having two sets of field poles, oneof said sets of poles being arranged to produce a substantially constantvoltage between said auxiliary brush and one of said load brushes andthe other of said sets of poles being arranged so that the armaturereaction varies the flux therein and produces a voltage between. saidauxiliary brush and the other load brush which varies with the armaturereaction, the voltage between the load brushes being equal to thealgebraic sum of the voltages between said auxiliary brush and each ofsaid load brushes and varying when the load current varies and a fieldwinding on said first mentioned set of poles connected between saidauxiliary brush and one of said load brushes.

10. In a constant speed dynamo-electric machine, an armature providedwith a commutator, load brushes and an auxiliary brush bearing on saidcommutator, a field magnet structure having two sets of field poles, oneof said sets of poles being arranged to produce a substantially constantvoltage between said auxiliary brush and one of said load brushes andthe other of said sets of poles being arranged so that the armaturereaction varies the flux therein and produces a voltage between saidauxiliary brush and the other load brush which varies with the armaturereaction, the voltage between the load brushes being equal to thealgebraic sum of the voltages between said auxiliary brush and each ofsaid load brushes and decreasing when the load current increases, and afield winding on said first mentioned set of poles connected betweensaid auxiliary brush and one of said load brushes.

11. An electrical system comprising an inherently regulated self-exciteddynamo-electric machine having an n pole armature winding and fieldstructure comprising 2 n mechanical field poles arranged in two setswith an equal number of poles in each set, adjacent poles of separatesets being arranged to be of like polarity, at least three brushescooperating with said armature,two of said brushes being spacedsubstantially 180 electrical degrees apart and arranged with respect tosaid poles so that the voltage between said brushes is dependent on theflux in both of said sets of poles, the third brush being arranged withrespect to said poles so that the voltage between said third brush andone of said 180 degree brushes is dependent of the fiux'in one only ofsaid sets of poles, an exciting winding for the inherently regulatedself-excited dynamo electric machine having an a pole armature windingand a field structure comprising 2 n mechanical field poles arranged intwo sets with an equal number of poles in each set, adjacent poles ofseparate sets being arranged to be of like polarity, at least threebrushes cooperating with said. armature, two of said brushes beingspaced substantially 180 electrical degrees apart and arranged withrespect to said poles so that the voltage between said brushes isdependend on the flux in both of said sets of poles, the third brushbeing arranged with respect to said poles so that the voltage betweensaid third brush and one of said 180 degree brushes is dependent on theflux in one only of said sets of poles, anexciting winding for the setof poles last mentioned connected to be supplied by two of said brushes,a load circuit connected across said 180 degree brushes, themachinebeing constructed and arranged so that the flux in 5 said set ofpoles last mentioned is not varied by cross magnetization due to loadcurrent,

the other set of poles being arranged to

